Materials characterization

The crystalline structure of the as-synthesized m-BiVO₄ was determined by X-ray diffraction (XRD) pattern using a X-ray diffraction spectrometer (Bruker AXS D2 Phaser) with a CuKα target (λ = 0.15418 nm, 40 kV and 100 mA) in the 2ϴ range of 10–80° at a scan rate of 1°/min. Laser Raman spectra were recorded using a Raman spectrometer (JOBIN YVON LabRam HR S8000U) excited with the 632.8 nm line of red laser at an 10 mW incident power. Optical absorption spectra were recorded using a UV–Vis spectrometer (Hitachi U-3300). The X-ray photoelectron spectra (XPS) were recorded on a XPS spectrometer (HRXPS-PHI Quantera SXM, Φ ULVAC-PHI, INC) at room temperature. The binding energy reference was taken at 284.7 eV for the C1s peak arising from the surface hydrocarbons. Prior to SEM analysis, the m-BiVO₄ NPs were dispersed in ethanol and small drops of suspended solution were kept on a Si wafer piece and dried in vacuum oven. The surface morphology and sample composition were determined using a field emission scanning electron microscope (FE-SEM; JEOL JSM-7000F) attached with an energy dispersive X-ray spectroscopy analyser (EDS; OXFORD Instruments, INCA PentaFETx3, Model 7,557). Prior to TEM analysis, the m-BiVO₄ NPs were dispersed in ethanol using an ultrasonicator and dropped onto a copper grid and dried in vacuum oven. The transmission electron microscopy (TEM). high-resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED) patterns were recorded using a JEOL JEM-2100 with an accelerating voltage of 80 kV and 200 kV, respectively. The time-evolved photocatalytic degradation of MB was measured by a T60 UV–Visible spectrophotometer (PG INSTRUMENTS LIMITED). The toxicity of raw and treated MB solutions were tested by Zebrafish embryo, the images of Zebrafish embryo were captured by a high resolution microscope (OLYMPUS 1X71, Lenses EW 10 x /22) attached with a Canon camera (EOS 650D).